Supertramp has songs, such as "School", "The Logical Song", and "Crime Of The Century", that head straight for the cynical end and never look back. However, they have had songs like "Give a Little Bit" that are more idealistic.
Nikki Sixx's "Life is Beautiful" says it right at the beginning: "Nothing like a trail of blood to find your way back home."
Morrissey of The Smiths is notorious for his cynical, jaded, navel gazing lyrics that end up somewhere on the far end of cynicism. Standouts include "Heaven Knows I'm Miserable Now", "Girlfriend in a Coma", and "That Joke Isn't Funny Anymore". Even his more romantic track, "There is a Light That Never Goes Out" is tinged with black humor.
John Lennon went to both sides quite readily. His first solo album, Plastic Ono Band, is generally seen as the "cynical" one, coming as it did as a result of his primal scream therapy, and his second album, Imagine, as the "idealistic" one (especially the title track) where he learned how to dress up his political statements and purging of personal demons in a way that people would accept them. (Indeed, "Imagine" is so idealistic that a lot of people miss just how radical its lyrics are.) The principle doesn't hold true for every song on the album (Imagine, for example, still includes the more cynical "Crippled Inside" and the Paul attack song "How Do You Sleep," and Plastic Ono Band has stuff like "Love") but as a whole, it's fairly accurate.
Opera has run all over the scale, depending a lot on the composer and the genre:
With Greek mythology as the typical source material, early operas were often very cynical - at least those that weren't Bowdlerized with a tacked-on Happy Ending.** Mozart's operas generally fall on the more idealistic end of the scale, with The Magic Flute as the standout among his oeuvre, but even the initially-cynical Don Giovanni ends up idealistic when the titular character's Karma Houdini antics finally end with him being dragged down to hell for his misdeeds. Cosi fan tutte is an exception to the rule, falling pretty far over on the cynical end despite being a comedy. The cynical Don Alfonso is proven right at the end when Fiordiligi and Dorabella are coerced into cheating on their fiancés, and pretty much no one except him ends up happy.
In Italian and French opera, whether the ending is more cynical or idealistic falls pretty strictly along dramatic/comedy lines. Even mostly light-hearted dramas usually had cynical endings. A common theme was showing two young, optimistic lovers progressing through their romance and getting closer and closer to achieving domestic bliss with each other - and then Shooting the Shaggy Dog by having one of them contract a disease and drop dead (see: La Traviata, Manon, La Bohème). Another was having one person be Driven to Suicide or murder by their lover's infidelity/cruelty/general dickishness (for example, Madame Butterfly, Carmen).
Opera in general took a hard turn for the cynical with the 20th century. Many of the titans of modern opera - Strauss's Salome and Elektra, Berg's Wozzeck and Lulu, Britten's Peter Grimes - fall on the extreme cynical end.
While Lyrical Dissonance and relative obscurity give the Barenaked Ladies a reputation for whimsical cheerfulness and humour (and it's there), their actual songs and lyrics often, arguably more often than not, fall very much on the Cynical side. For example, their songs involving love are decidedly realistic, not to mention numerous songs about PTSD or depression and the like.
Devo tends toward the cynical side in their concept of "De-evolution." According to former member Bob Lewis, however, there is something of an philosophical divide between the group's two frontmen, Mark Mothersbaugh and Jerry Casale:
"Gerry [sic] continues to strive for political statement and “high-concept” art, still maintaining some modernist, or perhaps more accurately, anti-postmodernist tendencies...Mark, on the other hand, has gained recognition for essentially commercial pursuits...his fine art prints continue to reflect his introspective highly personal aesthetic, which make their statements in a “small genre” manner; Mark IS postmodern." 
The Protomen. So far on the cynical side that they almost fall off the end. Yes, while singing about Mega Man.
Gorillaz is known to lean on the cynical end of the scale, particularly in Feel Good Inc.
Leonard Cohen's "Diamonds In The Mine" is one of the most depressing songs in terms of cynicism, with the lyrics describing life as one Shoot the Shaggy Dog moment after another.
"Only a Lad" by Oingo Boingo lands on the cynical side of the scale as the adults blame society for the way Johnny (the "Lad" in the song") behaves, as opposed to putting him in jail for killing people and stealing their stuff.
Tom Waits comes down heavily on the cynical side every single time. "Tom Traubert's Blues", "Rain Dogs", "God's Away On Business", you name it. He even managed to make "Heigh Ho" from Snow White bleak and dystopian in his cover of it.
Run-DMC's "It's Like That" flies all over the scale. You can't change the system, money's the most important thing you will need (when was the last time love bought you clothes?), the world seems to grow steadily crappier, life is shitty and you die - It's like that, and that's the way it is. But you shouldn't add to the misery and heartbreak life gives you - learn, don't be a fool, and help. Because it's like that, and that's the way it is.
David Bowie's creator thumbprints tend to come from the cynical end of existence — inevitable apocalypses and dystopias that can't be redeemed are common subject matter, and those who are mentally unstable, lonely, disadvantaged, and/or alienated from others have trouble finding a shoulder to cry on if they're not being outright persecuted or abused. "Black Tie White Noise" thumbs its nose at idealistic visions of race relations in favor of the Family-Unfriendly Aesop "Racial harmony won't come without a lot of pain and violence along the way." Even his most famous love song, ""Heroes"", acknowledges that the love in question may well not last. If there's a major optimistic message running through his body of work, it's probably "Enjoy what happiness you find while you can."
Ego Likeness is on the cynical side, often employing Humans Are the Real Monsters and Crapsack World in their songs. Burn Witch Burn, Funny Olde World, Song For Samael, Weave are good examples of this and even the somewhat uplifting Save Your Serpent have cynical lyrics.
Despite being one of, if not the, instigators of Heavy Metal, with lyrics involving dystopias and apocalyptic/satanic imagery, the band Black Sabbath and later Ozzy's solo career actually fluctuates between a middle-ground and somewhat idealistic. They might be talking about war and Satan and the end of the world, but they're talking about how war is *bad*, how Satan is going after *bad folks*, and how the end of the world *could* be. There's hope if people actually act decently to each other, but then again, their songs edge back towards cynicism with other themes.
Frightened Rabbit's the Oil Slick humorously starts on the Cynical side: the narrator wants to write a love song for his girl, but he can only write depressing songs. Halfway through, it switches to an Arcade Fire-esque section where he ultimately winds up on the idealistic side, as he realizes that the sad songs make him who he is, and he will have to own it and live through it. That section is a GIGANTIC Heartwarming Moment, especially after the depression of most of the album.
Speaking of depression, The National lie firmly on the cynical side, more so when it comes to their second album.
Power Metal is known for generally being very idealistic compared to most metal. whenever it is themed around the battle of good-versus-evil (Especially the ones with high-fantasy themes), good usually wins, though sometimes some sacrifices will have to be made along the way. Sci-fi-themed power-metal, on the other hand, is usually more cynical, generally being based around dystopian cyberpunk sorts of themes.